Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 222243 AAA
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
242 PM PST MON DEC 22 2014

UPDATED MARINE WATCHES/WARNINGS/ADVISORIES

.SHORT TERM...MOIST NORTHWEST FLOW WILL BRING SOME CONTINUED
SCATTERED LIGHT SHOWERS INTO THE AREA, MAINLY FROM THE CASCADES
WEST, THROUGH THIS EVENING. SHOWER ACTIVITY WILL DECREASE, EXCEPT
FOR A SOME CONTINUED LIGHT SHOWERS ALONG PORTIONS OF THE COAST
TONIGHT INTO TUESDAY MORNING AS AN UPPER RIDGE BUILDS INTO THE
AREA. THEN TUESDAY EVENING THROUGH WEDNESDAY MORNING, A COLD
UPPER TROUGH IS FORECAST TO DROP DOWN FROM THE NORTHWEST, BECOMING
POSITIONED OFF THE SOUTHERN OREGON COAST WEDNESDAY MORNING. THIS
TROUGH WILL BRING A SHARP FRONT INTO THE AREA WEDNESDAY WITH
PRECIPITATION SPREADING ACROSS THE AREA...FOLLOWED BY A COLD
SHOWERY AIRMASS MOVING INLAND BEHIND THE FRONT ON CHRISTMAS EVE,
WEDNESDAY EVENING.

MODELS HAVE TRENDED FASTER WITH THE MOVEMENT OF THE FRONT ON, SO
HAVE INCREASED THE CHANCE FOR PRECIPITATION OVER THE AREA TUESDAY
NIGHT THROUGH WEDNESDAY. AHEAD OF THE FRONT ON WEDNESDAY, EXPECT RAIN
TO SPREAD INTO THE AREA WITH SNOW ABOVE 6000 FT ELEVATION. GUSTY
SOUTHWEST WINDS ARE ALSO EXPECTED OVER THE MOUNTAINS AND INTO THE
SUMMER LAKE AREA WEDNESDAY AS 700 MB WINDS ALOFT INCREASE TO 40 TO
55 KT. THEN BEHIND THE FRONT, STRONG NORTHWEST FLOW ALOFT WILL
MOVE INTO THE AREA ALONG WITH THE COLD UPPER TROUGH. SNOW LEVELS
ARE EXPECTED TO DROP QUICKLY BEHIND THE FRONT FROM 6000 FT
ELEVATION AND HIGHER WEDNESDAY AFTERNOON...DOWN TO 2500 TO 3500
FEET ELEVATION WEDNESDAY EVENING FOR AREAS FROM THE CASCADES WEST
AND TO 4000 TO 5000 FT ELEVATION ELSEWHERE. SNOW LEVELS WILL LOWER
FURTHER TO 2000 TO 3000 FT WEDNESDAY NIGHT.

THE LOWERED SNOW LEVELS COMBINED WITH FORECAST SHOWERS WEDNESDAY
EVENING AREA EXPECTED TO BRING LIGHT SNOW ACCUMULATIONS OF 1 TO 3
INCHES TO THE MOUNTAINS ABOVE 3000 FT WITH 3 TO 6 INCHES ABOVE
6000 FT ELEVATION IN THE CASCADES. ALSO LIGHT SNOW ACCUMULATIONS
UP TO AN INCH ARE POSSIBLE IN SOME EAST SIDE VALLEYS WEDNESDAY
EVENING. ADDITIONAL LIGHT SNOW ACCUMULATIONS OF AROUND A TRACE TO
A HALF INCH ARE POSSIBLE OVERNIGHT WEDNESDAY AND ON CHRISTMAS
MORNING FOR ELEVATIONS DOWN TO 2000 FT FROM THE CASCADES WEST AS
THE TROUGH SHIFTS EAST BUT A LIGHT SHOWERY AIRMASS PERSISTS OVER
THE AREA. THIS MAY BRING A WHITE CHRISTMAS TO A FEW AREAS WEST OF
THE CASCADES AS WELL, MAINLY IN THE FOOTHILLS OF THE SISKIYOUS
AND CASCADES.

COLD AIR WILL PERSIST OVER THE AREA ON CHRISTMAS DAY WITH SNOW
LEVELS AROUND 2500 TO 3000 FT AND COOL TEMPERATURES. ALSO MODELS
SHOW A WEAK DISTURBANCE MOVING INTO NORTHWEST PORTIONS OF THE AREA
DURING THE DAY ON CHRISTMAS AND INTO THE NIGHT WITH ADDITIONAL
LIGHT SHOWERS POSSIBLE, MAINLY FROM THE COAST, INTO THE UMPQUA
AND INTO SOUTHERN OREGON CASCADES.

.LONG TERM...FRIDAY THROUGH MONDAY NIGHT...THERE IS A FAIR AMOUNT OF
UNCERTAINTY REGARDING THE LONG TERM, MOSTLY AS A RESULT OF A CLOSED
LOW THAT MODELS EXPECT TO DEVELOP JUST NORTH OF HAWAII EARLIER IN
THE WEEK. HOW THIS LOW BEHAVES, AS WELL AS WHERE EXACTLY IT TAKES UP
RESIDENCE, WILL HAVE A MARKED INFLUENCE ON THE WEATHER HERE IN THE
PACIFIC NORTHWEST. THE STRONGER THIS LOW IS, THE MORE AMPLIFIED THE
RIDGE DOWNSTREAM WILL BE; THE FARTHER WEST, THE MORE LIKELY THIS
RIDGE WILL MOVE IN OVER THE WEST COAST. WITH THIS IN MIND, HAVE
OPTED TO TREND THE FORECAST TOWARDS A BLEND OF THE GFS AND ECMWF
MODEL SOLUTIONS, AS THE TWO ARE SIMILAR, AND HAVE COME MORE INTO
LINE WITH ONE ANOTHER OVER THE PAST 24 HOURS.

THE RESULT WILL BE A WET AND COLD FORECAST LATE IN THE WEEKEND AND
INTO EARLY NEXT WEEK. THE AFOREMENTIONED RIDGE IS EXPECTED TO ALIGN
ITSELF WITH ROUGHLY 140 DEGREES WEST, WHICH THEN PLACES OUR AREA
WITHIN GENERALLY NORTHWEST FLOW, KEEPING THE AIR MASS OVERHEAD MOIST
AND COOL INTO FRIDAY NIGHT. A POTENT WAVE WILL TOP THE RIDGE, THEN
DROP SOUTH INTO SOUTHERN OREGON AND NORTHERN CALIFORNIA SATURDAY
INTO SUNDAY, RESULTING IN YET ANOTHER SHOT OF PRECIPITATION FOR THE
ENTIRE FORECAST AREA. SNOW LEVELS DURING THIS TIME ARE EXPECTED TO
BE RELATIVELY LOW, HOVERING SOMEWHERE BETWEEN 3000 AND 4000 FEET,
WHICH WOULD MEAN MUCH OF THE PRECIPITATION OVER THE MOUNTAINS AND
MOST OF THE PASSES IN THE AREA WILL FALL AS SNOW. IN OTHER WORDS,
THERE WILL BE A POTENTIAL FOR TRAVEL ISSUES DURING THE WEEKEND
FOLLOWING CHRISTMAS. THIS WILL BEAR WATCHING OVER THE NEXT SEVERAL
FORECAST CYCLES. THE TROUGH WILL ALSO BRING MUCH COLDER AIR TO THE
REGION, DROPPING TEMPERATURES TO BELOW SEASONAL NORMALS. THIS COLD
AIR WOULD THEN REMAIN IN PLACE THROUGH THE END OF THE TERM, ALTHOUGH
RIDGING EARLY NEXT WEEK MAY BUMP THEM BACK UP TO NORMAL OR ABOVE.


&&

.AVIATION...FOR THE 22/18Z TAF CYCLE...A FEW AREAS OF LIGHT RAIN
WILL CONTINUE OVER THE REGION TODAY...MAINLY OVER THE HIGHER
TERRAIN. MOUNTAIN OBSCURATION WILL REMAIN WIDESPREAD THROUGH THE
DAY. A MIXED BAG OF IFR...MVFR...AND VFR CEILINGS IS EXPECTED...WITH
THE LOWEST CEILINGS EXPECTED AT THE COAST AND INTO THE UMPQUA
VALLEY. TONIGHT...MOST VALLEY LOCATIONS WILL DEGRADE TO IFR WITH LOW
CEILINGS AND FOG. -BPN

&&

.MARINE...UPDATED 215 PM PST MON DEC 22 2014...WEAK HIGH PRESSURE
WILL REMAIN OVER THE WATERS THROUGH TUESDAY RESULTING IN RELATIVELY
LIGHT AND VARIABLE WINDS. HOWEVER...MODERATE WEST SWELL WILL
CONTINUE. MODELS ARE IN BETTER AGREEMENT AS TO WINDS ASSOCIATED WITH
A MODERATE COLD FRONT EXPECTED TO MOVE THROUGH WEDNESDAY. THE FRONT
WILL BE QUICK MOVING, SO WHILE WE MAY HAVE A BRIEF PERIOD OF SMALL
CRAFT ADVISORY LEVEL SOUTH WINDS AHEAD OF IT, THE STRONGEST WINDS
ARE EXPECTED BEHIND THE FRONT WITH NORTH GALES POSSIBLE WEDNESDAY
MORNING THROUGH EARLY EVENING. THE MAIN QUESTION REMAINING IS THE
EXACT TIMING OF THE FRONT. WE`VE ISSUED A GALE WATCH AND HAZARDOUS
SEAS WATCH FOR MUCH OF WEDNESDAY TO COVER THIS POTENTIAL. -WRIGHT

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...GALE WATCH FROM WEDNESDAY AFTERNOON THROUGH
WEDNESDAY EVENING   FOR PZZ350-356-370-376.
HAZARDOUS SEAS WATCH FROM WEDNESDAY AFTERNOON THROUGH
    WEDNESDAY EVENING FOR PZZ350-356-370-376.
    SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 PM PST
    WEDNESDAY FOR PZZ350-356-376.
    SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 1 PM PST WEDNESDAY
  FOR PZZ370.

$$

CC



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